In DVD (Digital Versatile Disc) video standards, interactive operations can be performed, that is, users can switch sound or subtitles when playing back AV (Audio Visual) content, such as a movie, recorded in a recording medium (for example, see Non-Patent Document 1). More specifically, the user operates a sound switch button 11 or a subtitle switch button 12 of a remote controller 2 to switch sound or subtitles of AV content displayed on a display device 1 shown in FIG. 1. For example, if the user operates the sound switch button 11 when sound 1 is set in the initial state in the display device 1, sound 1 is switched to sound 2, as shown in FIG. 2.
AV content based on the DVD video is recorded in the form of a MPEG (Moving Picture Experts Group) 2 program stream. In the MPEG2 program stream, as shown in FIG. 3, a video stream (indicated by “video” in FIG. 3), a plurality of audio streams (indicated by “audio 1”, “audio 2”, and “audio 3” in FIG. 3), and a plurality of sub-picture streams (indicated by “sub-picture 1, “sub-picture 2”, and “sub-picture 3”) are multiplexed such that the audio streams and the sub-picture streams are AV-synchronized with the video stream. The sub-picture streams (sub-pictures 1, 2, and 3) are streams in which bitmap images are run-length coded, and are mainly used for subtitles.
Generally, a plurality of audio streams are used for recording sound of different languages, and a plurality of sub-picture streams are used for recording subtitles of different languages. The user can interactively select sound or subtitles of a desired language by using the remote controller 2 while video is being played back.
The DVD video defines a table structure, provided to users, indicating the relationship between sound numbers and subtitle numbers for a plurality of audio streams (audio 1, 2, and 3) and a plurality of sub-picture streams (sub-pictures 1, 2, and 3) in a program stream.
FIG. 4 illustrates an example of such a stream number table indicating the relationship between audio signals and subtitle signals provided to the user. In this table, the sound numbers are referred to as “A_SN (Audio Stream Numbers)”, and the subtitle numbers are referred to as “S_SN (Sub-picture Stream Numbers)”. In the stream number table shown in FIG. 4, each of the audio streams is provided with A_SN, and each of the sub-picture streams is provided with S_SN. A_SN=1: audio 2, A_SN=2: audio 1, and A_SN-3: audio 3. Also, S_SN=1: sub-picture 3, S_SN=2: sub-picture 1, and S_SN=3: sub-picture 2. In this case, a smaller number of A_SN or S_SN indicates an audio signal or a subtitle signal to be provided to users with higher priority. That is, A_SN=1 is an audio stream played back as a default, and S_SN=L is a sub-picture stream played back as a default.
More specifically, sound 1 played back in the initial state in FIG. 1 is audio 2, which is A_SN=1 (FIG. 4), and sound 2 played back after being switched from sound 1 in FIG. 2 is audio 1, which is A_SN=2.
[Non-Patent Document 1]
DVD Specifications for Read-Only Disc Part 3; Version
A technique for using Sub Paths to play back sound which is additionally recorded (so-called “dubbed sound”) is known (for example, see Patent Document 1).
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. 2002-158972.